This invention relates to a method and apparatus for dissipating impact energy between relative converging members. More particularly the invention relates to a method and apparatus for dissipating energy imparted to a protective marine bumper from impact forces imparted thereto by a floating vessel or the like.
In the past in both onshore and offshort locations some form of fendering or protective bumper system has been utilized to dissipate kinetic energies imparted from a floating vessel into a relatively stationary mooring or berthing facility. Such devices may range from the expedient utilization of a worn out tire casing to elaborate elastomeric cellular fendering units of a variant and often intricate configuration.
While such systems have exhibited at least a degree of utility in protecting moored vessels from damage, room for significant improvement remains. In this connection elastomeric units typically exhibit a somewhat linear sloping stroke/force relationship at least during initial impact loading. Therefore it is necessay to design for large deflections in order to dissipate high energy impact loads. Further upon full compression elastomeric units typically exhibit a recoil or rebound force which is transmitted back into the floating vessel. Still further elastomeric designs which are operable to efficiently accommodate cyclic low load levels such as wave action induced forces are often unsuited to dissipate high level impact energies occasioned during a berthing maneuver.
The problems enumerated in the foregoing are not intended to be exhaustive but rather are among many which tend to impair the effectiveness of the previously known energy dissipation systems. Other noteworthy problems may also exist, however, those presented in the discussion above should be sufficient to demonstrate that marine cushioning systems appearing in the art have not been altogether satisfactory. An energy dissipation assembly according to the present invention is intended to at least obviate or minimize problems of the type previously noted.
More specifically the subject invention is directed to an improved method and apparatus for dissipating energy, preferably in a marine bumper system, wherein a piston and a cylinder assembly is connected at the ends thereof between a protective bumper and a marine installation such as an onshore pier, an offshore berthing dolphin, an offshore tower leg, etc.
The hydraulic cylinder is comprised of an inner generally circular high pressure cylinder which is operable to receive in intimate translation a piston body. The high pressure cylinder is provided with a plurality of radially extending exponentially spaced metering ports whereby fluid from within the interior of the cylinder may be metered into a surrounding low pressure return chamber formed by a relatively thin cylindrical wall coaxially mounted about the high pressure cylinder.
Approximately a first 20 percent of the stroke of the piston body is merely impeded by metering fluid within the high pressure cylinder through unvalved ports and back into the high pressure cylinder upon the opposite side of the piston body assembly through a return port. Such low level impedance is highly effective to dissipate cyclic wave action induced forces.
The remaining 80 percent of the exponentially spaced ports are preferably fitted with normally closed preset pressure relief or check valve assemblies which are actuated to an open posture only upon achieving a predetermined quantum of impact energy. Further, each of the present check valve units has maximum capacity limits and is operable to accommodate extremely high level impact forces which may be occassioned during an accidental high velocity berthing operation.
The hydraulic cushioning assembly is isolated from a hostile ambient marine environment by the provision of an encapsulating cylindrical housing connected at the ends thereof to the hydraulic unit through annular generally frustoconically shaped elastomeric members.
The isolation housing is axially dimensioned so as to place the elastomeric units under bending and shear loading even during full extension of the hydraulic cushioning unit. Accordingly once impact energy forces have been dissipated metering of fluid through the hydraulic cylinder wall, restoring forces provided by the flex and shear of the elastomeric units rapidly restore the cushioning unit to an extended posture ready to receive and dissipate further impact energies. A further metering port, however, is positioned adjacent the restoring end of the cylinder to eliminate any rapid rebound energy from the elastomeric members.
The method entails the steps of isolating the piston and cylinder assembly from a hostile corrosive marine environment while cushioning low level impact forces against the marine protective bumper by flexing and shearing the elastomeric annulus members and translating the piston body within the high pressure cylinder. The method further includes the steps of restoring the piston body to a position of axial extension by application of the developed flex and shear of the elastomeric annulus members while metering fluid from behind the piston body through the wall of the high pressure fluid cylinder. Such metering of fluid during the restoration step effectively minimizes or eliminates the possibility of rebound energy being input to the floating vessel.
Through the provision of the instant hydraulic cushioning assembly it has been found that cushioning of kinetic energies in a marine environment including low level cyclic wave action forces, normal impact berthing energy and excessive impact energy is effected by a force level diagram of near optimum performance and efficiency.
Further, the exterior housing effectively isolates the hydraulic cushioning unit from a hostile and corrosive marine environment while synergistically providing a highly efficient restoring mechanism for maintaining the cushioning unit in an extended posture operable to receive and dissipate impact energy.
In presenting the invention, reference will now be made to a preferred embodiment. This preferred embodiment is by way of illustration and not restriction or limitation with respect to the present invention and the manner in which it may be practiced.